How can I run Gazebo and the real PR2 simultaneously?

Hello, I try to run a Gazebo simulation of a physical environment and the (real) PR2 at the same time. Running the PR2 first and launching Gazebo then leads to a broken PR2 connection (Dashboard disconnects..). I suppose this is mainly because of Gazebo sets 'use_sim_time' to true on the param server and publishes on the /clock topic. My question is then actually if someone tried something similar already or has any ideas or hints to bring me on the right track. BTW I want to validate robot actions in simulation before executing them. Thanks a lot.